Kidney disease spans the spectrum of acute, chronic, and end-stage disease. Acute renal failure is associated with a high rate of short-term adverse events but its incidence and long-term sequelae have not been well delineated. Chronic renal insufficiency affects millions of Americans but we are only now beginning to appreciate its broad clinical and public health significance. End-stage renal disease incidence continues to increase relentlessly in the U.S. but the forces driving this have not been fully elucidated. Studying the complex links between acute, chronic and end-stage renal disease will refine our understanding of the scope and natural history of renal disease and improve risk stratification. To address these issues, we propose to assemble and follow prospectively a very large, unique cohort of adults who have renal function measures and are receiving comprehensive care within Kaiser Permanente of Northern California, a large integrated healthcare delivery system. Supplemental unbiased ascertainment of death and end-stage renal disease treatment will be captured by cross-linkage with national registries such as the National Death Index as well as the U.S. Renal Data System. We have three specific aims: Aim #1 : To determine the rate of renal function loss and long-term outcomes in a representative population of patients with chronic renal insufficiency. Aim #2: To evaluate the impact of chronic renal insufficiency severity on risk of acute renal failure. Aim #3: To determine whether episodes of acute renal failure accelerate the course of chronic renal insufficiency towards end-stage renal disease. Our research plan will overcome methodological obstacles to address these important questions. We propose a cost-effective and rigorous approach through leveraging multiple, complementary automated databases and targeted chart review within a diverse and representative population. Better understanding of [unreadable] the epidemiology and natural history of chronic renal insufficiency and the impact of acute renal failure will lead to improved patient management and better public health policies. [unreadable] [unreadable] [unreadable]